Structure characterization of an exopolysaccharide produced by Bifidobacterium animalis RH.

An exopolysaccharide fraction (EPSb) produced by Bifidobacterium animalis RH isolated from the feces of centenarians was purified to illustrate its structure and conformational characterization. Results from Fourier-transform infrared spectrometry, gel permeation chromatography, high-pH anion-exchange chromatography with pulsed amperometric detection, periodate oxidation and Smith degradation, methylation and gas chromatography-mass spectrometry, and nuclear magnetic response analysis indicated that EPSb (M(w)=21.3 kDa) was composed of rhamnose (Rha), arabinose (Ara), galactose (Gal), glucose (Glc), and mannose (Man) in a molar ratio of 0.4:0.3:1.6:0.8:1.2. This compound had a backbone of (1→3,4)-linked Man, (1→4)-linked Rha, (1→4)-linked Gal, and (1→4)-linked Glc. It was branched with Gal and terminated with Gal and Glc residues. The molecular structure of EPSb was observed via atomic force microscopy. EPSb showed spherical lumps and a ring-like network. Conformational analysis revealed the non-triple helical conformation of EPSb.